The corneal endothelium is known to play an important role in maintaining the corneal transparency. The proposal is made to elucidate the mechanism(s) responsible for the corneal transparency by investigating: 1) ion movements across the rabbit corneal endothelium; 2) apical and basolateral membrane permeabilities of endothelial cells; 3) intracellular and trans-endothelial impedance. The effects of ouabain, amiloride, 2-4-6 triaminopyrimidine, SITS, DIDS, furosemide, vanadate, and trypsin on the movements of sodium, potassium, chloride, and bicarbonate across the preparation will be investigated. The isotope flux measurements are a continuation of ongoing projects that utilize the novel, most useful, revealing presteady-state, flux measuring technique. In order to learn about the membrane properties, the membrane potential difference and the intracellular ionic (sodium, potassium, bicarbonate, hydrogen) concentrations will be measured as a function of the concentrations of the above mentioned drugs in he external solution. Both conventional and ion selective microelectrodes will be used for this purpose. The impedance measurements are expected to yield valuable information about the surface charge on the apical and basolateral membranes. A newly developed method utilizing a computer will be employed in the intracellular and trans-endothelial impedance measurements. A pseudorandom noise current pulse is applied across the corneal endothelium. Shielded intracellular and trans-endothelial microelectrodes retrieve the response signals, which are then transformed into a frequency domain by a fast Fourier transformation. The transformed signals are further processed to get the auto- and cross-correlation spectral functions from which in turn the transfer function (impedance) is obtained.